1. Field
The following description relates generally to wireless network communications, and more particularly to channel sounding over multiple antenna ports.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as, for example, voice, data, and so on. Typical wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple-access systems may include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as third generation partnership project (3GPP), 3GPP long term evolution (LTE), ultra mobile broadband (UMB), evolution data optimized (EV-DO), etc.
Generally, wireless multiple-access communication systems may simultaneously support communication for multiple mobile devices. Each mobile device may communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to base stations. Further, communications between mobile devices and base stations may be established via single-input single-output (SISO) systems, multiple-input single-output (MISO) systems, multiple-input multiple-output (MIMO) systems, and so forth.
In one example, a mobile device can communicate with the base station using multiple antenna ports and can apply a precoder to MIMO communications sent to a base station to maximize capacity of channels to the base station over the multiple antenna ports. For example, the base station can determine channel conditions with the mobile device (e.g., based on previous communications therewith), and can indicate the precoder to the mobile device in light of the determined channel conditions. The mobile device can receive and apply the precoder to subsequent communications for transmitting over the multiple antenna ports.
Channel conditions can change, however, and the base station may not always specify the optimal precoder for current conditions. In some cases, the mobile device transmits a demodulation reference signal (DM-RS) with uplink communications that specifies parameters for demodulating the uplink communications, and this can be used to determine channel conditions. In MIMO communications, however, the mobile device may not always use all antenna ports to transmit the DM-RS (or can combine antenna ports such that multiple antenna ports transmit the same DM-RS), which can impact the base station's ability to determine conditions over all channels for selecting a precoder.